Problem: Numeric Excel fields automatically read as Double
When adding an Excel sheet to ArcMap, numeric fields default to the Double type.
Field types specified in Excel are not read by ArcGIS. Instead, the field types are determined by reading the first eight rows for that field. If mixed data types are found in a single field, that field is returned as a string and the values are converted to strings. If the values are found to be numeric, the field is returned as a Double.
Solution or Workaround
Currently, Excel fields can only be converted to one of two types, String or Double. To change the field type, the sheet must be converted to a read/write table format such as dBase IV, CSV, or geodatabase tables.
In Excel, select File > Save As. Select a supported format from the choices available in Excel and click 'Yes' when Excel warns that certain formatting is not supported in this file format.
Exit Excel. Click 'No' when Excel prompts to save the changes.
Open the new table in ArcMap.
Right-click on the table in the Table of Contents and select Open.
From the Table Options drop-down menu, select Add Field and specify a Name and Field Type.
Right-click the new field and select the Field Calculator option. Select 'Yes' if prompted to work outside an edit session.
Calculate the new field equal to the existing numeric field.